On 8/27/19 5:45 PM, Fernando Pacheco wrote:
During normal driver unload we attempt to disable GuC communication
while it is currently stopped. This results in a nop'd call to
intel_guc_ct_disable within guc_disable_communication because
stop/disable rely on the same flag to prevent further comms with CT.

We can avoid the call to disable and still leave communication in a
satisfactory state by extracting a set of shared steps from stop/disable.
This set can include guc_disable_interrupts as we do not require the
single caller of guc_stop_communication to be atomic:
"drm/i915/selftests: Fixup atomic reset checking".

This situation (stop -> disable) only occurs during intel_uc_fini_hw,
so during fini, call guc_disable_communication only if currently enabled.
The symmetric calls to enable/disable remain unmodified for all other
scenarios.

Signed-off-by: Fernando Pacheco <[email protected]>
Cc: Chris Wilson <[email protected]>
Cc: Michal Wajdeczko <[email protected]>
Cc: Daniele Ceraolo Spurio <[email protected]>
---
  drivers/gpu/drm/i915/gt/uc/intel_uc.c | 30 ++++++++++++++++-----------
  1 file changed, 18 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/uc/intel_uc.c 
b/drivers/gpu/drm/i915/gt/uc/intel_uc.c
index 71ee7ab035cc..29a9eec60d2e 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_uc.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_uc.c
@@ -224,17 +224,7 @@ static int guc_enable_communication(struct intel_guc *guc)
        return 0;
  }
-static void guc_stop_communication(struct intel_guc *guc)
-{
-       intel_guc_ct_stop(&guc->ct);
-
-       guc->send = intel_guc_send_nop;
-       guc->handler = intel_guc_to_host_event_handler_nop;
-
-       guc_clear_mmio_msg(guc);
-}
-
-static void guc_disable_communication(struct intel_guc *guc)
+static void __guc_stop_communication(struct intel_guc *guc)
  {
        /*
         * Events generated during or after CT disable are logged by guc in
@@ -247,6 +237,20 @@ static void guc_disable_communication(struct intel_guc 
*guc)
guc->send = intel_guc_send_nop;
        guc->handler = intel_guc_to_host_event_handler_nop;
+}
+
+static void guc_stop_communication(struct intel_guc *guc)
+{
+       intel_guc_ct_stop(&guc->ct);
+

The only difference between intel_guc_ct_stop() and intel_guc_ct_disable() is that in the latter we also tell guc that we've disabled the buffers. We could probably just add a check to return early if !intel_guc_is_running() in intel_guc_ct_disable() and drop the stop/disable differentiation entirely, but that doesn't need to happen in this patch.


+       __guc_stop_communication(guc);
+
+       DRM_INFO("GuC communication stopped\n");
+}
+
+static void guc_disable_communication(struct intel_guc *guc)
+{

Are we now guaranteed that guc_disable_communication() is called only of communication is actually enabled? if so, we could add here a:

        GEM_BUG_ON(!guc_communication_enabled(guc));

with or without that:

Reviewed-by: Daniele Ceraolo Spurio <[email protected]>

Daniele

+       __guc_stop_communication(guc);
intel_guc_ct_disable(&guc->ct); @@ -537,7 +541,9 @@ void intel_uc_fini_hw(struct intel_uc *uc)
        if (intel_uc_supports_guc_submission(uc))
                intel_guc_submission_disable(guc);
- guc_disable_communication(guc);
+       if (guc_communication_enabled(guc))
+               guc_disable_communication(guc);
+
        __uc_sanitize(uc);
  }
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